Introduction:

The relative mass of an object is how many times more massive the object
is than a standard object. The atomic masses of atoms are all relative masses.
They can be considered relative to any particular element. Historically,
both oxygen and carbon have served as the reference standard. For our purposes
we can also consider atomic masses relative to the least massive
element--hydrogen, with an atomic mass of approximately one. Fluorine, with
a relative mass of 19, is 19 times more massive than hydrogen, etc. In this
laboratory exercise you deal with the relative masses of beans. Then you
will be asked to draw a parallel to the atomic masses of elements.

Purpose:

To develop an understanding of the mole concept and molar masses of elements
through an analogy with a model system.

Safety:

Just don't spill the beans!

Procedure:

Part I. Be sure to use the same balance for the entire activity.

In a beaker, count out exactly 100 beans of one type. Discard any beans that
differ greatly from an average bean. If you fail to do this, your results
will not be accurate.

Put a plastic cup on the electronic balance. Hit the tare button.

Add the beans to the cup; record their mass to the nearest 0.01 g.

Each team member is responsible for one type of bean provided.

Calculations:

Calculate (do not weigh) the mass of one bean of each type. Record the value
in the data table. [Note: "Calculate" means to take the total mass of 100
beans and divide by 100 rather than weighing one particular bean.]

Determine the relative mass of each type of bean.

Relative Mass = (Average mass of one bean/Average mass of the lightest type
of bean)

Calculate the number of beans in one relative mass of each bean. Do this
by dividing the relative mass by the average mass of one bean.

Number of beans is = ( one Relative mass/Average mass of one bean)

Check your calculated results in Step 7 by following these steps:

Place the plastic cup on the balance pan and hit the tare button.

Add beans of your type until the balance contains one relative
mass of your type bean.

Count the beans. Record this as the measured number of beans in one relative
mass.

Pour the beans into a pile. Retain your separate piles of relative masses
of beans. You will answer questions about them later.

Each team member is responsible for his or her type bean.

Data Analysis and Concept Development:

Questions:

What did you find out about the number of beans in one relative mass?
( ) same ( ) different

How do your calculated values compare to your measured values?
( ) same (within one bean) ( ) different

Compare the volume of the relative mass piles.
( ) same ( ) different Why?___________________________

a. What is the average mass of the lightest bean?______________g

b. What is the relative mass of the lightest bean?_____________g

Among the elements, hydrogen has the least massive atoms an atom of hydrogen
has an average mass of 1.66 x 10--24 g. This is very small, but remember
it is only one atom! What is the relative
mass of hydrogen if it is the least massive element? _____________g

Part II.

Below is a chart reporting the average masses of individual atoms. Calculate
the relative mass of each element and record it in the chart. Then look up
the molar mass (atomic mass) of each element on a periodic table and record
it in the table.

How do the atomic masses found on the periodic table compare to the relative
masses you calculated?
( ) same ( ) different

What did you find out about the number of atoms of each element in one relative
mass?
( ) same ( ) different